Gripping devices are well known and widely used in a variety of applications. For example, industrial applications such as component assembly, packaging, and shipping to name a few. In recent years, robotic applications and other automated processes have proliferated to virtually all aspects of the manufacturing and production. Even in the sales environment, automated machinery is fast replacing human labor to store and retrieve inventory products stocked in warehouses. In the foregoing and other similar applications, various gripping devices are used for handling parts and products.
As will be discussed further below, the present invention is generally directed to gripping devices of the type having a pair of opposing gripping jaws that operate by moving the jaws in an opposing fashion to grip an article. Although a tremendous variety of these types of devices are known, the prior art devices can be generally characterized by opposing gripping jaws operated in a linear fashion by some-type of driving mechanism. This driving mechanism is often in the form of a piston, or pistons, that is driven to reciprocate in a cylinder, wherein the pistons are attached to the gripping jaws so that reciprocation of the pistons serves to reciprocate the gripping jaws. Controlling the reciprocation of the pistons,-in turn, controls the operation of the jaws. Furthermore, reciprocation of the pistons is often controlled by applying fluid pressure to the pistons.
All of the piston-driven prior art, of which applicant is aware, includes what is known as "double acting" pistons. Such double acting pistons operate by applying both the driving and return forces to the same end of the piston. As a result, the driving and return forces are unbalanced. That is, the jaws are usually driven with a greater force in the driving (gripping) direction and lesser force in the return direction. This driving/return force imbalance is known to occur as a result of asymmetric fluid chamber configurations (i.e., the driving chamber and the return chamber).
In uni-directional applications (i.e., applications where the gripping jaws are operative in only one direction), the driving force imbalance is not a problem. However, in bi-directional applications, wherein both inside and outside gripping surfaces are provided on the gripping devices (allowing the gripping device to grip some articles by driving the jaws together to grip the outside of the article or, alternatively, driving the jaws apart to grip the article by an inside edge), unbalanced piston driving forces may be problematic.
Much of the prior art is also characterized by what is known as a "slide and gib" configuration. In this configuration, a mechanical linkage is attached between the driving piston and the gripping jaws, laterally displacing the gripping jaws from the driving piston. As a result, a bending moment is introduced into the structure. It is appreciated that the bending moment increases with increasing length of the mechanical linkage.